| 1. |
- Aghion, S., et al.
(författare)
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A moiré deflectometer for antimatter
- 2014
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- The precise measurement of forces is one way to obtain deep insight into the fundamental interactions present in nature. In the context of neutral antimatter, the gravitational interaction is of high interest, potentially revealing new forces that violate the weak equivalence principle. Here we report on a successful extension of a tool from atom optics—the moiré deflectometer—for a measurement of the acceleration of slow antiprotons. The setup consists of two identical transmission gratings and a spatially resolving emulsion detector for antiproton annihilations. Absolute referencing of the observed antimatter pattern with a photon pattern experiencing no deflection allows the direct inference of forces present. The concept is also straightforwardly applicable to antihydrogen measurements as pursued by the AEgIS collaboration. The combination of these very different techniques from high energy and atomic physics opens a very promising route to the direct detection of the gravitational acceleration of neutral antimatter.
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| 2. |
- Ariga, T., et al.
(författare)
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Measuring GBAR with emulsion detector
- 2014
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Ingår i: International Journal of Modern Physics, Conference Series. - : World Scientific. - 2010-1945. ; 30
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Belaineh, Dagmawi, et al.
(författare)
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Controlling the Organization of PEDOT:PSS on Cellulose Structures
- 2019
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Ingår i: ACS APPLIED POLYMER MATERIALS. - : AMER CHEMICAL SOC. - 2637-6105. ; 1:9, s. 2342-2351
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Tidskriftsartikel (refereegranskat)abstract
- Composites of biopolymers and conducting polymers are emerging as promising candidates for a green technological future and are actively being explored in various applications, such as in energy storage, bioelectronics, and thermoelectrics. While the device characteristics of these composites have been actively investigated, there is limited knowledge concerning the fundamental intracomponent interactions and the modes of molecular structuring. Here, by use of cellulose and poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), it is shown that the chemical and structural makeup of the surfaces of the composite components are critical factors that determine the materials organization at relevant dimensions. AFM, TEM, and GIVVAXS measurements show that when mixed with cellulose nanofibrils, PEDOT:PSS organizes into continuous nanosized beadlike structures with an average diameter of 13 nm on the nanofibrils. In contrast, when PEDOT:PSS is blended with molecular cellulose, a phase-segregated conducting network morphology is reached, with a distinctly relatively lower electric conductivity. These results provide insight into the mechanisms of PEDOT:PSS crystallization and may have significant implications for the design of conducting biopolymer composites for a vast array of applications.
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| 4. |
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| 5. |
- Berggren, Johanna, et al.
(författare)
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Revascularization of Free Skin Grafts Overlying Modified Hughes Tarsoconjunctival Flaps Monitored Using Laser-Based Techniques
- 2019
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Ingår i: Ophthalmic Plastic and Reconstructive Surgery. - 1537-2677. ; 35:4, s. 378-382
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: It has recently been shown that the flap pedicle does not supply blood to a tarsoconjunctival graft in the modified Hughes procedure in patients. This raises questions concerning the rate of revascularization of the free skin graft commonly used to reconstruct the anterior lamella. The aim of this study was, thus, to monitor the course of revascularization in free skin grafts overlying modified Hughes tarsoconjunctival flaps, using laser-based techniques.Methods: Free skin grafts from the upper eyelid or upper arm in 9 patients were used to cover a tarsoconjunctival flap according to the modified Hughes procedure. Blood perfusion was monitored using laser speckle contrast imaging, and vascular reactivity was studied with laser Doppler velocimetry after heating the tissue to 44°C. Measurements were made at the time of surgery (baseline) and at 1, 3, 8, and 16 weeks postoperatively.Results: The gradual increase in perfusion of the free skin grafts during the healing process indicates revascularization. A slight increase in perfusion was seen already after 1 week. Perfusion reached 50% of the baseline after 3 weeks, and complete restoration of perfusion was seen after 8 weeks. The vascular function monitored with heat-induced hyperemia increased in a similar fashion.Conclusions: Full-thickness skin grafts revascularize within 3 to 8 weeks, despite overlying a tarsoconjunctival flap, which has recently been reported to be avascular. This provides further evidence that it should be possible to repair large eyelid defects using free full-thickness eyelid grafts.
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| 6. |
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| 7. |
- Berggren, Karl, 1989-, et al.
(författare)
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Characterization of photon-counting multislit breast tomosynthesis
- 2018
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Ingår i: Medical Physics. - : John Wiley & Sons. - 2473-4209 .- 0094-2405.
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: It has been shown that breast tomosynthesis may improve sensitivity and specificity compared to two-dimensional mammography, resulting in increased detection-rate of cancers or lowered call-back rates. The purpose of this study is to characterize a spectral photon-counting multislit breast tomosynthesis system that is able to do single-scan spectral imaging with multiple collimated x-ray beams. The system differs in many aspects compared to conventional tomosynthesis using energyintegrating flat-panel detectors. Methods: The investigated system was a prototype consisting of a dual-threshold photon-counting detector with 21 collimated line detectors scanning across the compressed breast. A review of the system is done in terms of detector, acquisition geometry, and reconstruction methods. Three reconstruction methods were used, simple back-projection, filtered back-projection and an iterative algebraic reconstruction technique. The image quality was evaluated by measuring the modulation transfer-function (MTF), normalized noise-power spectrum, detective quantum-efficiency (DQE), and artifact spread-function (ASF) on reconstructed spectral tomosynthesis images for a total-energy bin (defined by a low-energy threshold calibrated to remove electronic noise) and for a high-energy bin (with a threshold calibrated to split the spectrum in roughly equal parts). Acquisition was performed using a 29 kVp W/Al x-ray spectrum at a 0.24 mGy exposure. Results: The difference in MTF between the two energy bins was negligible, that is, there was no energy dependence on resolution. The MTF dropped to 50% at 1.5 lp/mm to 2.3 lp/mm in the scan direction and 2.4 lp/mm to 3.3 lp/mm in the slit direction, depending on the reconstruction method. The full width at half maximum of the ASF was found to range from 13.8 mm to 18.0 mm for the different reconstruction methods. The zero-frequency DQE of the system was found to be 0.72. The fraction of counts in the high-energy bin was measured to be 59% of the total detected spectrum. Scantimes ranged from 4 s to 16.5 s depending on voltage and current settings. Conclusions: The characterized system generates spectral tomosynthesis images with a dual-energy photon-counting detector. Measurements show a high DQE, enabling high image quality at a low dose, which is beneficial for low-dose applications such as screening. The single-scan spectral images open up for applications such as quantitative material decomposition and contrast-enhanced tomosynthesis.
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| 8. |
- Berggren, Karl-Fredrik
(författare)
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All-Time High
- 2010
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Ingår i: Fysikaktuellt. - 0283-9148. ; :4, s. 3-3
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 9. |
- Berggren, Karl-Fredrik, et al.
(författare)
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Basic Modeling of Openness, Quantum States and Transport in Two- and Three-Dimensional Ballistic Cavities
- 2010
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Ingår i: Journal of Siberian Federal University. Mathematics & Physics. ; 3, s. 280-288
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Tidskriftsartikel (refereegranskat)abstract
- A basic model for particle states and current flow in open quantum dots/billiards are investigated. The model is unconventional and extends the use of complex potentials first introduced in phenomenological nuclear inelastic scattering theory (the optical model). Attached leads/source drain are represented by complex potentials. Probability densities and currents flows for open 2D quantum dots/billiards are calculated and the results are compared with microwave measurements used to emulate the dot. We also apply the model to a recangular enclosure and report on helical flows guided by nodal lines and disc-like accumulations of flow lines. The model is of conceptual as well as practical and educational interest.
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| 10. |
- Berggren, Karl-Fredrik, et al.
(författare)
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Basic modelling of transport in 2D wave-mechanical nanodots and billiards with balanced gain and loss mediated by complex potentials
- 2018
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Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 30:20
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Tidskriftsartikel (refereegranskat)abstract
- Non-Hermitian quantum mechanics with parity-time (PT) symmetry is presently gaining great interest, especially within the fields of photonics and optics. Here, we give a brief overview of low-dimensional semiconductor nanodevices using the example of a quantum dot with input and output leads, which are mimicked by imaginary potentials for gain and loss, and how wave functions, particle flow, coalescence of levels and associated breaking of PT symmetry may be analysed within such a framework. Special attention is given to the presence of exceptional points and symmetry breaking. Related features for musical string instruments and wolf-notes are outlined briefly with suggestions for further experiments.
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